From: Russell Currey ruscur@russell.cc
commit 3c12b4df8d5e026345a19886ae375b3ebc33c0b6 upstream.
The mitigation-patching.sh script in the powerpc selftests toggles all mitigations on and off simultaneously, revealing that rfi_flush and stf_barrier cannot safely operate at the same time due to races in updating the static key.
On some systems, the static key code throws a warning and the kernel remains functional. On others, the kernel will hang or crash.
Fix this by slapping on a mutex.
Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt") Cc: stable@vger.kernel.org # v5.14+ Signed-off-by: Russell Currey ruscur@russell.cc Acked-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20211027072410.40950-1-ruscur@russell.cc Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/lib/feature-fixups.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -228,6 +228,7 @@ static void do_stf_exit_barrier_fixups(e
static bool stf_exit_reentrant = false; static bool rfi_exit_reentrant = false; +static DEFINE_MUTEX(exit_flush_lock);
static int __do_stf_barrier_fixups(void *data) { @@ -253,6 +254,9 @@ void do_stf_barrier_fixups(enum stf_barr * low level interrupt exit code before patching. After the patching, * if allowed, then flip the branch to allow fast exits. */ + + // Prevent static key update races with do_rfi_flush_fixups() + mutex_lock(&exit_flush_lock); static_branch_enable(&interrupt_exit_not_reentrant);
stop_machine(__do_stf_barrier_fixups, &types, NULL); @@ -264,6 +268,8 @@ void do_stf_barrier_fixups(enum stf_barr
if (stf_exit_reentrant && rfi_exit_reentrant) static_branch_disable(&interrupt_exit_not_reentrant); + + mutex_unlock(&exit_flush_lock); }
void do_uaccess_flush_fixups(enum l1d_flush_type types) @@ -486,6 +492,9 @@ void do_rfi_flush_fixups(enum l1d_flush_ * without stop_machine, so this could be achieved with a broadcast * IPI instead, but this matches the stf sequence. */ + + // Prevent static key update races with do_stf_barrier_fixups() + mutex_lock(&exit_flush_lock); static_branch_enable(&interrupt_exit_not_reentrant);
stop_machine(__do_rfi_flush_fixups, &types, NULL); @@ -497,6 +506,8 @@ void do_rfi_flush_fixups(enum l1d_flush_
if (stf_exit_reentrant && rfi_exit_reentrant) static_branch_disable(&interrupt_exit_not_reentrant); + + mutex_unlock(&exit_flush_lock); }
void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_end)